Uniplanar bone screw

ABSTRACT

A uniplanar bone anchor including a housing and a bone screw is provided. The lower region of the housing defines mating elements that mate with engaging elements on the bone screw to limit movement of the housing relative to the bone screw to a single plane.

PRIORITY APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/243,992, filed on Apr. 3, 2014, which application is incorporatedherein by reference in its entirety.

TECHNICAL FIELD

The disclosure is directed to vertebral anchors for use with orthopedicfixation systems. More particularly, the disclosure is directed touniplanar bone anchors.

BACKGROUND

The spinal column of a patient includes a plurality of vertebrae linkedto one another by facet joints and an intervertebral disc locatedbetween adjacent vertebrae. The facet joints and intervertebral discallow one vertebra to move relative to an adjacent vertebra, providingthe spinal column a range of motion. Diseased, degenerated, damaged, orotherwise impaired facet joints and/or intervertebral discs may causethe patient to experience pain or discomfort and/or loss of motion, thusprompting surgery to alleviate the pain and/or restore motion of thespinal column.

One possible method of treating these conditions is to immobilize aportion of the spine to allow treatment. Traditionally, immobilizationhas been accomplished by rigid stabilization. For example, in aconventional spinal fusion procedure, a surgeon restores the alignmentof the spine or the disc space between vertebrae by installing a rigidfixation rod between pedicle screws secured to adjacent vertebrae. Bonegraft is placed between the vertebrae, and the fixation rod cooperateswith the screws to immobilize the two vertebrae relative to each otherso that the bone graft may fuse with the vertebrae.

In some cases, it may be desirable to use an anchor that provides arange of motion in only one plane.

SUMMARY

The disclosure is directed to several alternative designs, materials andmethods of assembling uniplanar bone anchor structures and assemblies.

In one example, a uniplanar bone anchor may include a housing and a bonescrew, where the housing has a bore with a longitudinal axis, the boreextending through the housing to a lower opening, the housing includinga channel for receiving an elongate member, the channel extendingtransverse to the bore. The bone screw may have a longitudinal axis andmay include a head and a shank extending from the head, the bone screwmay be configured to extend through the bore with the head positionablein the housing and the shank extending from the lower opening of thehousing, the head having a substantially spherical surface with planarsurfaces on opposing sides of the head. The housing may include at leastone mating element extending from an inner surface of the housing intothe bore, transverse to the longitudinal axis of the housing, the atleast one mating element configured to couple with the planar surfaceson the screw head such that the bone screw is moveable relative to thehousing with the longitudinal axis of the bone screw being positionablein any one of a plurality of angular positions within a single planerelative to the longitudinal axis of the bore.

In some examples, the mating element may be a single element and mayinclude two opposing planar surfaces extending parallel to thelongitudinal axis of the housing. The mating element may extend into thebore along an entire circumference of the inner surface of the housing,and an opening in the mating element may define the planar surfaces. Insome examples, the opposing planar surfaces may be separated by opposingcurved surfaces.

In another example, bone anchor may include a housing having a boreextending therethrough defining an inner surface and a channel extendingtransverse to the bore, and a mating element extending from an innersurface of the housing into the bore, the mating element includingopposing planar surfaces, and a bone screw including a head and a shankextending from the head, the screw positionable within the housing suchthat the screw head resides in the housing and the shaft extends outsidethe housing, the screw head having a spherical surface with opposingplanar surfaces configured to mate with the opposing planar surfaces ofthe housing, wherein mating of the opposing planar surfaces on the screwhead and the housing results in uniplanar movement of the housingrelative to the bone screw, the inner surface of the housing includingcurved surfaces capable of slidably coupling with the spherical surfaceof the bone screw head, wherein the inner surface of at least a lowerend of the housing includes threading extending across the curvedsurfaces and the opposing planar surfaces.

In another example, a bone anchor may include a housing having a boreextending through the housing from an upper end to a lower end, thehousing having a channel extending transverse to the bore, the housingincluding at least one mating element, and a bone screw including a headand a shank extending from the head, the head positionable within thehousing, the head having at least one engaging element configured tomate with the at least one mating element on the housing to limit motionof the bone screw relative to the housing to a single plane, and aninner surface of at least the lower end of the housing may includethreading.

The above summary of some examples is not intended to describe eachdisclosed example or every implementation of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may be more completely understood in consideration of thefollowing detailed description of various examples in connection withthe accompanying drawings, in which:

FIG. 1 is a perspective exploded view of components of an exemplary boneanchor;

FIG. 2 is a side view of the bone screw of FIG. 1;

FIG. 3 is a side view of the bone screw of FIG. 1 transverse to the viewof FIG. 2;

FIG. 4 is a perspective view of the insert of the apparatus of FIG. 1.

FIG. 5 is a cross-sectional partially elevated view of the housing ofthe anchor of FIG. 1;

FIG. 6 is a cross-sectional view of the assembled anchor of FIG. 1, withphantom lines showing alternate positions of the screw;

FIG. 7 is a cross-sectional view of the assembled anchor of FIG. 1transverse to the cross-sectional view of FIG. 6;

FIG. 8 is a perspective view of the assembled bone anchor of FIG. 1,without the housing;

FIG. 9 is a perspective exploded view of components of another exemplarybone anchor;

FIG. 10 is a side view of the bone screw of FIG. 9;

FIG. 11 is a side view of the bone screw of FIG. 9 transverse to theview of FIG. 10;

FIG. 12 is a perspective view of the insert of the apparatus of FIG. 9;

FIG. 13 is a cross-sectional partially elevated view of the housing ofthe anchor of FIG. 9;

FIG. 14 is a top view of the housing of FIG. 9;

FIG. 15 is a side view of the assembled bone anchor of FIG. 9, withoutthe housing;

FIG. 16 is a cross-sectional view of the assembled bone anchor of FIG.9; and

FIG. 17 is a cross-sectional view of the assembled bone anchor of FIG. 9transverse to the cross-sectional view of FIG. 16.

FIG. 18 is a perspective exploded view of components of anotherexemplary bone anchor;

FIG. 19 is a cross-sectional exploded view of the bone anchor of FIG.18;

FIG. 20 is a perspective view of the insert of FIG. 18;

FIG. 21 is a cross-sectional partially elevated view of the housing ofFIG. 18;

FIG. 22 is a cross-sectional view of the assembled bone anchor of FIG.18;

FIG. 23 is a cropped cross-sectional view of the assembled bone anchorof FIG. 18 transverse to the cross-sectional view of FIG. 22;

FIG. 24 is an exploded elevational view of components of anotherexemplary bone anchor;

FIG. 25 is a perspective view of the insert of FIG. 24;

FIG. 26 is a cross-sectional view of the housing of FIG. 24;

FIG. 27 is a cross-sectional view of the housing of FIG. 24 transverseto the cross-sectional view of FIG. 26; and

FIG. 28 is a cross-sectional view of the assembled bone anchor of FIG.24.

While the invention is amenable to various modifications and alternativeforms, specifics thereof have been shown by way of example in thedrawings and will be described in detail. It should be understood,however, that the intention is not to limit aspects of the invention tothe particular examples described. On the contrary, the intention is tocover all modifications, equivalents, and alternatives falling withinthe spirit and scope of the invention.

DETAILED DESCRIPTION

For the following defined terms, these definitions shall be applied,unless a different definition is given in the claims or elsewhere inthis specification.

All numeric values are herein assumed to be modified by the term“about”, whether or not explicitly indicated. The term “about” generallyrefers to a range of numbers that one of skill in the art would considerequivalent to the recited value (i.e., having the same function orresult). In many instances, the term “about” may be indicative asincluding numbers that are rounded to the nearest significant figure.

The recitation of numerical ranges by endpoints includes all numberswithin that range (e.g., 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4,and 5).

Although some suitable dimensions, ranges and/or values pertaining tovarious components, features and/or specifications are disclosed, one ofskill in the art, incited by the present disclosure, would understanddesired dimensions, ranges and/or values may deviate from thoseexpressly disclosed.

As used in this specification and the appended claims, the singularforms “a”, “an”, and “the” include plural referents unless the contentclearly dictates otherwise. As used in this specification and theappended claims, the term “or” is generally employed in its senseincluding “and/or” unless the content clearly dictates otherwise.

As used in this specification, the term “top” refers to the portion ofthe figure or element closer the top of the page, and the term “bottom”refers to the portion of the figure or element closer to the bottom ofthe page.

The following detailed description should be read with reference to thedrawings in which similar elements in different drawings are numberedthe same. The detailed description and the drawings, which are notnecessarily to scale, depict illustrative examples and are not intendedto limit the scope of the invention. The illustrative examples depictedare intended only as exemplary. Selected features of any illustrativeexample may be incorporated into an additional example unless clearlystated to the contrary.

A uniplanar bone anchor allows for movement of a housing relative to abone screw in only a single plane. Structural elements on the screw headand the interior of the housing may provide the uniplanar movement. Thescrew may be bottom loading or top loading. FIGS. 1-8 illustrate abottom loading bone screw, FIGS. 9-17 illustrate a first example of atop loading bone screw. FIGS. 18-23 illustrate a second example of a toploading bone screw, and FIGS. 24-28 illustrate a third example of a toploading bone screw.

FIG. 1 is an exploded view illustrating components of an exemplary boneanchor 10. The bone anchor 10 may include a housing 30, a bone screw 20,and a retainer assembly 13. Bone anchor 10 may be referred to as abottom loading system, with the bone screw 20 inserted through thebottom of the housing 30. In use, the bone anchor 10, which may bescrewed into a vertebra, may serve to couple a rod or other elongatemember (not shown) extending along a portion of a spinal column. The rodor elongate member may fit into a U-shaped channel 43 formed by opposingarms 41 of the housing 30. The channel 43 may extend along a transverseor horizontal axis. The bone anchor 10 may include particular degrees ofadjustability within a single plane, ensuring that, when multiple boneanchors are used with a single rod, each screw may be locked down at theparticular locations and orientations desired by the practitioner, andthe housings may be adjusted to a desired position within the singleplane to receive the rod.

It should be noted that in practice, even though the screw 20 may befirst screwed into the vertebra, then the housing 30 may be adjusted toaccommodate a rod in the U-shaped channel 43, in this document weexamine the elements from the point of view of the housing 30, so thatthe screw 20 may be referred to as being adjustable with respect to thehousing 30. The housing has a longitudinal axis L-L as seen in FIG. 1,which may be considered to be a vertical axis. A transverse orhorizontal axis along which the channel 43 lies may extend transverse tothe longitudinal axis L-L. The longitudinal axis L-L, bisects a verticalplane. The screw 20 may be moveable relative to the housing 30 with thelongitudinal axis of the screw 20 being positionable in any one of aplurality of angular positions within the vertical plane relative to thelongitudinal axis of the housing bore, as seen in FIG. 6. The screw 20and housing 30 may thus be moveable relative to each other in a singleplane. The screw 120, 220, 320 and housing 130, 230, 330 shown in FIGS.9-28 also exhibit uniplanar movement.

As shown in FIGS. 1-3, the screw 20 may have a threaded shank 23configured to extend out the bottom opening of the housing 30 and engagea vertebra. The screw 20 may be a monolithic, single piece structurehaving a longitudinal axis L-L, as shown in FIG. 1. The screw 20 mayhave a head 21 that is generally spherical in shape with opposing planarsurfaces 25 and a driver interface such as a keyed portion 22. Thestructure of the housing 30 and retainer assembly 13 in combination withthe planar surfaces 25 on the screw head 21 may allow pivoting of thescrew head 21 in a single plane with respect to the housing 30.

As seen in FIG. 5, the housing 30 may be monolithic, thus formed as asingle piece. In other examples the housing 30 may be formed of multiplepieces that are connected prior to use. The housing 30 may have a bore44 extending through the housing 30 along the longitudinal axis L-L ofthe housing, transverse to the U-shaped channel 43. The screw 20 may bereceived in the bore 44. Threading 42 may be provided on the innersurface of the arms 41 for connection with a fastener or set screw (notshown). The housing 30 may include additional features such as recesses33 or grooves 35 for interaction with insertion tools, extensionsleeves, reduction tools, etc. The housing 30 may have a generallycircular opening 56 in the bottom surface 51 of the housing, with theopening 56 sized and shaped to receive the screw head 21 for bottomloading.

The housing 30 may include a mating element 32 such as one or moreprotrusion extending from an inner wall of the housing 30 into the bore44, transverse to the longitudinal axis L-L, of the housing. The matingelement 32 may include a single mating element extending into the bore44 along an entire circumference of the inner surface of the housing 30,with an opening defining opposing planar surfaces 34 and opposing curvedsurfaces 36, as shown in FIGS. 5-7. The curved surfaces 36 may beconfigured to mate with the spherical surface of the screw head 21, andthe planar surfaces 34 may be configured to mate with the planarsurfaces 25 of the screw head 21. In some examples, the mating element32 may include discrete portions extending from an inner wall of thehousing 30 into the bore 44 (not shown). The mating element 32 may atleast partially define a lower chamber 38 and an upper chamber 39 withinthe housing 30. The screw head 21 may be received within the housing 30in a first orientation or a second orientation, turned 180 degrees fromthe first orientation. The mating of the planar surfaces 34 of thehousing with the planar surfaces 25 of the screw head 21 may preventrotation of the screw 20 around the longitudinal axis L-L. The mating ofthe curved surfaces 36 of the housing with the spherical surface of thescrew head 21 may allow movement of the screw head 21 within a singleplane. As shown in phantom in FIG. 6, the screw 20 may be moved within asingle plane to various positions relative to the housing 30.

The head 21 of the screw 20 may be held in place by a retainer assembly13, which may prevent the screw 20 from being removed through the bottomof the housing 30 once the screw is inserted. The retainer assembly 13may be in the form of one or more rings having a central aperture, whichmay allow the practitioner to insert a screwdriver through the apertureof the rings to engage a driver interface such as a keyed portion 22 onthe head 21 of the screw 20. The retainer assembly 13 may include aretaining ring 14, a wave washer or biasing member 15, and an insert 16.The exemplary retainer assembly 13 in FIG. 1 includes an insert 16 thatmay contact the head 21 of the screw 20, a biasing member 15, and aretaining ring 14. The retaining ring 14 may be a split ring, as shownin FIG. 1, or it may be a continuous ring. The biasing member 15 may bea wave washer. The retaining ring 14 may be received in the lowerchamber 38 of the housing 30, below the mating element 32. The retainingring 14 may contact a lower surface of the screw head 21, and mayprevent the screw 20 from exiting the housing 30 through the loweropening of the housing 30, as shown in FIG. 6.

As seen in FIGS. 4 and 6, the insert 16 may include a concave innerannular surface 50 that has a radius of curvature matched to that of thescrew head 21, so that when the housing 30 is pivoted relative to thescrew 20, it may remain held in place by the insert 16. The insert 16may have opposing planar surfaces 52 that, when aligned with the planarsurfaces 25 of the screw head 21, as shown in FIG. 8, may allow thescrew head 21 and insert 16 to fit within the interior of the housing30. The insert 16 may have a lower lip 55 that extends from the insert16 into the upper chamber 39 when the insert 16 is disposed on the screw20 within the housing 30. The biasing member 15 may be placed over theinsert 16 such that the biasing member resides above the lip 55. Thebiasing member 15 may aid in biasing the insert 16 and screw 20 towardsthe bottom surface 51 of the housing 30. The retainer assembly 13 maymaintain the screw 20 in the housing 30 in the absence of a rod. Oncethe screw 20 and retainer assembly 13 are disposed within the housing30, the retaining ring 114 may prevent the screw 20 from being removedthrough the bottom of the bore 44 and the biasing member 15 and insert16 may prevent the screw 20 from being removed through the top of thebore.

Another example of uniplanar bone anchor 100 is shown in FIGS. 9-17.FIG. 9 is an exploded view illustrating components of bone anchor 100.The bone anchor 100 may include a housing 130, a bone screw 120, and aretainer assembly 113. Bone anchor 100 may be referred to as a toploading system, with the bone screw 120 inserted through the top of thehousing 130. Similar to the bone anchor 10 described above, the boneanchor 100 may be screwed into a vertebra and may serve to couple a rodor other elongate member (not shown) extending along a portion of aspinal column. The rod or elongate member may fit into a U-shapedchannel 143 formed by opposing arms 141 of the housing 130. The boneanchor 100 may include particular degrees of adjustability within asingle plane, ensuring that, when multiple bone anchors are used with asingle rod, each screw may be locked down at the particular locationsand orientations desired by the practitioner, and the housings may beadjusted to a desired position within the single plane to receive therod.

As shown in FIGS. 9-11, the screw 120 may have a threaded shank 123configured to extend out the bottom opening of the housing 130 andengage a vertebra. The screw 120 may be a monolithic, single piecestructure. The screw 120 may have a head 121 that is generally sphericalin shape with opposing planar surfaces 125 and extensions 127. Theextensions 127 may follow the spherical surface of the head 121, withplanar surfaces 125 formed by removal of material under the extensions127. An undercut 129 may be formed under the extensions 127 such thatextensions 127 define an overhang or lip. The extensions 127 and planarsurfaces 125 may be on opposite sides of the screw head 121, as shown inFIGS. 10 and 11.

The retainer assembly 113 may be in the form of one or more rings havinga central aperture, which may allow the practitioner to insert ascrewdriver through the aperture of the rings to engage a driverinterface such as a keyed portion 122 on the head 121 of the screw 120.The exemplary retainer assembly 113 shown in FIGS. 9 and 15 includes aninsert 116 that may contact the head 121 of the screw 120, a biasingmember 115, and a retaining ring 114. The retaining ring 14 may be acontinuous ring, as shown in FIG. 9, or it may be a split ring. Thebiasing member 115 may be a wave washer as shown in FIG. 9. As seen inFIGS. 12 and 16, the insert 116 may include a concave inner annularsurface 150 that has a radius of curvature matched to that of the screwhead 121 so that when the screw 120 is pivoted within the housing 130,it may remain held in place by the insert 116. The insert 116 may havean annular lower lip 155. The structure of the housing 130 and retainerassembly 113 in combination with the planar surfaces 125 and extensions127 on the screw head 121 may allow pivoting of the screw head 121 in asingle plane with respect to the housing 130.

As seen in FIG. 13, the housing 130 may be monolithic, thus formed as asingle piece. In other examples the housing 130 may be formed ofmultiple pieces that are connected prior to use. The housing 130 mayhave a bore 144 extending through the housing 130 along the longitudinalaxis L-L of the housing, transverse to the U-shaped channel 143. Thescrew 120 may be received in the bore 144 through the top of the housing130. Threading 142 may be provided on the inner surface of the arms 141for connection with a fastener or set screw (not shown). The housing 130may include additional features such as recesses 133 or grooves 135 forinteraction with insertion tools, extension sleeves, reduction tools,etc.

The housing 130 may include opposing mating elements 132 extending froman inner wall of the housing 130 into the bore 144, transverse to thelongitudinal axis L-L of the housing. The mating elements 132 mayinclude discrete portions extending from an inner wall of the housing130 into the bore 144 as seen in FIGS. 13 and 14. The mating elements132 may have opposing planar surfaces 134 extending along thelongitudinal axis L-L. The mating elements 132 may define upper surfaces146. The remaining inner surface of the inner wall at the bottom of thehousing may define opposing curved surfaces 136. The curved surfaces 136may be configured to mate with the spherical surface of the screw head121, and the planar surfaces 134 may be configured to mate with theplanar surfaces 125 of the screw head 121. The extensions 127 andassociated undercuts 129 on the screw head 121 may be configured to matewith the upper surfaces 146 of the mating elements 132. The mating ofthe planar surfaces 134 of the housing with the planar surfaces 125 ofthe screw head 121 may prevent rotation of the screw 120 around thelongitudinal axis L-L. The mating of the curved surfaces 136 of thehousing with the spherical surface of the screw head 121 may allowmovement of the screw head 121 within a single plane. As shown inphantom in FIG. 17, the screw 120 may be moved within a single plane tovarious positions relative to the housing 130.

The bone screw 120 may be inserted through the top of the housing 130with the threaded shank 123 extending out the bottom 151 of the housing130, as seen in FIGS. 16 and 17. The head 121 of the screw 120 may beheld in place by the retainer assembly 113. The mating of the extensions127 on the screw head 121 with the upper surfaces 146 of the housing mayprevent the screw 120 from being removed through the bottom of thehousing 130. As seen in FIGS. 16 and 17, the retaining ring 114 andbiasing member 115 are received in an annular space 117 defined betweenan inner wall of the housing 130 and the insert 116, above a lower lip155 on the insert 116.

To lock the elements in place, the practitioner may screw a fastener orset screw (not shown) into threading 42, 142 at the upper portion of thehousing 30, 130, which may force the rod or elongate member against theupper surface of insert 16, 116, and in turn may force the insert 16,116 against the head 21, 121 of the screw 20, 120. Prior to finaltightening of the set screw, the biasing member 15, 115 may cause theinsert 16, 116 to frictionally engage the head 21, 121 of the screw 20,120 to resist movement of the housing 30, 130 with respect to the screw20, 120. After tightening of the set screw, the frictional force betweenthe insert 16, 116 of the retainer assembly 13, 113 and the head 21, 121of the screw 20, 120 may be sufficient to lock the screw 20, 120 inplace with respect to the housing 30, 130. In some examples, theU-shaped channel 43, 143 may be deep enough so that the set screw doesnot force the rod against the bottom of the U-shaped channel 43, 143.Alternatively, the retainer assembly 13, 113 may be omitted, and the setscrew may force the rod directly against the head 21, 121 of the screw20, 120 to secure the screw 20, 120 in place.

Another example of top loading uniplanar bone anchor 200 is shown inFIGS. 18-23. FIG. 18 is an exploded view illustrating components of boneanchor 200. The bone anchor 200 may include a housing 230, a bone screw220, and a retainer assembly 213. Bone anchor 200 may be referred to asa top loading system, with the bone screw 220 inserted through the topof the housing 230. Similar to the bone anchor 100 described above, thebone anchor 200 may be screwed into a vertebra and may serve to couple arod or other elongate member (not shown) extending along a portion of aspinal column. The rod or elongate member may fit into a U-shapedchannel 243 formed by opposing arms 241 of the housing 230. The boneanchor 200 may include particular degrees of adjustability within asingle plane, ensuring that, when multiple bone anchors are used with asingle rod, each screw may be locked down at the particular locationsand orientations desired by the practitioner, and the housings may beadjusted to a desired position within the single plane to receive therod. The structure of the housing 230 and retainer assembly 213 incombination with openings 225 in the screw head 221, openings 245 in thehousing 230, and pins 227 may allow pivoting of the screw head 221 in asingle plane with respect to the housing 230.

As shown in FIGS. 18-19, the screw 220 may have a threaded shank 223configured to extend out the bottom opening of the housing 230 andengage a vertebra. The screw 220 may be a monolithic, single piecestructure. The screw 220 may have a head 221 that is generally sphericalin shape with a pair of diametrically opposed openings 225 extendinginto the head 221 transverse to the longitudinal axis L of the boneanchor 200. The openings 225 are sized and configured to receive pins227. The pins 227 may have a outer portion 228 and an inner portion 229,with the outer portion 228 having a larger diameter than the innerportion 229. See FIG. 19. The openings 245 in the housing may be sizedto receive the outer portions 228 with a friction fit. The openings 225in the screw head 221 may have a diameter greater than the diameter ofthe inner portion 229, allowing for a gap between the inner portion 229and the inner wall of the opening 225, which may provide for somelongitudinal movement of the screw head 221 relative to the pins 227.See FIG. 22. In another example bone anchor a single pin 227 may be usedwith a housing 230 having one opening 245 and a bone screw 220 havingone opening 225. The single pin 227 may restrict movement of the screw220 relative to the housing 230 to a single plane.

The retainer assembly 213 may be in the form of one or more rings havinga central aperture, which may allow the practitioner to insert ascrewdriver through the aperture of the rings to engage a driverinterface such as a keyed portion 222 on the head 221 of the screw 220.The exemplary retainer assembly 213 shown in FIG. 18 includes an insert216 that may contact the head 221 of the screw 220, a biasing member215, and a retaining ring 214. The retaining ring 214 may be acontinuous ring, as shown in FIG. 18, or it may be a split ring. Thebiasing member 215 may be a wave washer as shown in FIG. 18. As seen inFIGS. 20 and 23, the insert 216 may include a concave inner annularsurface 250 that has a radius of curvature matched to that of the screwhead 221, so that when the screw 220 is pivoted within the housing 230,it may remain held in place by the insert 216. The insert 216 may have apair of diametrically opposed concave part cylindrical surfaces 260. Thesurfaces 260 may engage the rod when the surfaces 260 are aligned with achannel 243 in the housing 230 through which the rod extends. The insert216 may have a pair of diametrically opposed cut-outs 265 which mayallow the insert 216 to be positioned over the screw head 221 withoutinterfering with the insertion of the pins 227 into the openings 225 onthe screw head 221. The insert 216 may have an annular lower lip 255.The annular lower lip 255 may have a key feature such as an extension256, which mates with a corresponding key feature such as a recess 232in the housing 230. See FIG. 21.

As seen in FIG. 18, the housing 30 may be monolithic, thus formed as asingle piece. In other examples the housing 230 may be formed ofmultiple pieces that are connected prior to use. The housing 230 mayhave a bore 244 extending through the housing 230 along the longitudinalaxis of the housing, transverse to the U-shaped channel 243. The screw220 may be received in the bore 244 through the top of the housing 230.At least an upper portion of arms 241 may include threading 242 on aninner surface thereof. Threading 242 may have a form, pitch, and size toconform to the threads on a fastener such as a set screw (not shown).The inner surface of at least the lower portion of the housing 230 mayinclude threading 240 having a form, pitch, and size configured to allowthe threaded screw shank 223 to pass through. See FIGS. 19 and 21. Thethreading 240 inside the lower portion of the housing 230 may allow fora wide variety of screw diameters to be used. When a diameter of thescrew shaft is smaller than the inner diameter of the tower portion ofthe housing, the screw may be dropped through the bore 244 with only thescrew head 221 engaging the housing 230. The threading 240, however,allows for a larger diameter screw to be inserted. As a larger diameterscrew is inserted into the interior cavity of housing 230, the threading224 on the screw 220 include substantially the pitch to engage threading240 which extend through to the lower end of housing 230. In thismanner, a polyaxial screw 220 can be screwed into position until thescrew head 221 rests on the curved surface 236 at the lower portion ofthe housing 230. In some examples, threading 240 may extend from thelower end of threading 242.

This construction may allow a bone screw 220 having a larger shaft 223diameter than the bore 244 of the housing 230 to be insertedtherethrough, whereby the screw head 221 will still engage the seat 237of the housing. The thread form and pitch of the bone screw 220 do nothave to match the exact thread form and pitch of the housing 230 foroperation. The pitch and form of the threading 224 on the bone screwneed only be constructed and arranged to threadably pass through thebore 244 without significant interference between the two components.When a smaller diameter bone screw is used, there may be sufficientclearance between the outer diameter of the threading 224 and walls ofthe bore 244 to easily allow the screw to be inserted through the boreuntil the screw head 221 rests on the seat 237 of the housing 230. Solong as the screw head 221 remains the same size, this feature may alsoallow the interchangeability of screws of varying shaft 223 diameterwhile utilizing the same housing 230, retainer assembly 213, andfasteners or set screws (not shown). A kit may be provided whichincludes a housing 230, retainer assembly 213, and set screw (notshown), with a plurality of bone screws 220 having different outer shaftdiameters allowing a surgeon to choose a bone screw for the specificpatient condition.

The housing 230 may include additional features such as recesses 233and/or grooves 235 for interaction with insertion tools, extensionsleeves, reduction tools, etc.

The housing 230 may include a pair of diametrically opposed openings 245extending through the wall of the housing 230 into the bore 244,transverse to the longitudinal axis L-L of the housing. The openings 245are positioned such that when the screw head 221 is seated in the lowerportion of the housing 230, the openings 245 on the housing 230 may bealigned with the openings 225 on the screw head 221. Insertion of thepins 227 through the openings 245 and 225 allows the screw 220 to bemoved or pivoted within a single plane with respect to the housing 230.See FIG. 22. The diameter of the openings 245 in the housing 230 may beconfigured to receive the outer portion 228 of the pins 227 with afriction fit. The pins 227 have a length such that the second portionmay be seated within the opening 225 in the screw head 221 and the outerportion 228 extends into the opening 245 in the housing 230, as shown inFIG. 22. The slightly larger opening 225 compared to the inner portion229 of the pin 227 allows the screw head 221 to move distally when therod is inserted and tightened.

Insertion of the pins 227 through openings 245 of the housing andopenings 225 of the screw head 221 may prevent rotation of the screw 220around the longitudinal axis L-L, and in combination with the mating ofthe curved surface 236 of the housing with the spherical surface of thescrew head 221, may allow movement of the screw head 221 within a singleplane. As shown in phantom in FIG. 23, the pins 227 allow the screw 220to be moved within a single plane to various positions relative to thehousing 230.

The bone screw 220 may be inserted through the top of the housing 230with the threaded shank 223 extending out the bottom of the housing 230,as seen in FIGS. 21 and 23. The head 221 of the screw 220 may be held inplace by the retainer assembly 213. The insertion of the pins 227through the openings 245 in the housing 230 and into the openings 225 onthe screw head 221 may prevent the screw 220 from being removed throughthe bottom of the housing 230. As seen in FIGS. 21 and 23, the retainingring 214 and biasing member 215 are received in an annular space 217defined between an inner wall of the housing 230 and the insert 216,above a lower lip 255 on the insert 216.

Another example of uniplanar bone anchor 300 is shown in FIGS. 24-28.FIG. 24 is an exploded view illustrating components of bone anchor 300.The bone anchor 300 may include a housing 330, a bone screw 320, and aretainer assembly 313. Bone anchor 300 may be referred to as a toploading system, with the bone screw 320 inserted through the top of thehousing 330 as shown in FIG. 24. Similar to the bone anchors 10, 100,200 described above, the bone anchor 300 may be screwed into a vertebraand may serve to couple a rod or other elongate member (not shown)extending along a portion of a spinal column. The rod or elongate membermay fit into a U-shaped channel 343 formed by opposing arms 341 of thehousing 330. The bone anchor 300 may include particular degrees ofadjustability within a single plane, ensuring that, when multiple boneanchors are used with a single rod, each screw may be locked down at theparticular locations and orientations desired by the practitioner, andthe housings may be adjusted to a desired position within the singleplane to receive the rod.

The bone screw 320 may be similar in structure and function to the bonescrew 20 described above and shown in FIGS. 1-3. The screw 320 may havea threaded shank 323, a head 321 that is generally spherical in shapewith opposing planar surfaces 325, and a driver interface such as akeyed portion 322. The retainer assembly 313 may have a similarstructure and function as the retainer assembly 213 described above andshown in FIGS. 18-20. The retainer assembly 313 may include a retainingring 314, a biasing member 315, and an insert 316 with a concave innerannular surface 350 that has a radius of curvature matched to that ofthe screw head 321. The insert 316 may have a pair of diametricallyopposed concave part cylindrical surfaces 360 configured to engage therod when the surfaces 360 are aligned with a channel 343 in the housing330 through which the rod extends. The insert 316 may have opposingplanar surfaces 352 which may include cut-outs 365 that, when alignedwith the planar surfaces 325 of the screw head 321, may allow the screwhead 321 and insert 316 to fit within the interior of the housing 330.The insert 316 may have an annular lower lip 355 extending laterallyaway from the body of the insert, and may include a key feature such asan extension 356, which mates with a corresponding key feature such as arecess 332 in the housing 330. See FIGS. 25 and 26. The biasing member315 may be placed over the insert 316 such that the biasing memberresides above the lip 355. The biasing member 315 may aid in biasing theinsert 316 and screw 320 towards the bottom of the housing 330.

As seen in FIG. 26, the housing 330 may be monolithic, thus formed as asingle piece. In other examples the housing 330 may be formed ofmultiple pieces that are connected prior to use. The housing 330 mayhave a bore 344 extending through the housing 330 along the longitudinalaxis L-L of the housing, transverse to the U-shaped channel 343. Thescrew 320 may be received in the bore 344 through the top of the housing330. The housing may include a seat 337 extending partially into thebore 344 to prevent the screw 320 from being removed through the bottomof the housing 330. At least an upper portion of arms 341 may includethreading 342 on an inner surface thereof. Threading 342 may have aform, pitch, and size to conform to the threads on a fastener such as aset screw (not shown). The inner surface of at least the lower portionof the housing 330 may include threading 340 having a form, pitch, andsize configured to allow the threaded screw shank 323 to pass through.See FIGS. 26 and 27.

As discussed above with reference to the example shown in FIGS. 18-23,the threading 340 inside the lower portion of the housing 330 may allowfor a wide variety of screw diameters to be used. A smaller diameterscrew shaft may be dropped through the bore 344 with only the screw head321 engaging the housing 330, while a larger diameter screw with threads324 having substantially the pitch to engage threading 340 allows apolyaxial screw 320 to be screwed into position until the screw head 321rests on the seat 337 at the lower portion of the housing 330. In someexamples, threading 340 may extend from the lower end of threading 342.The thread form and pitch of the bone screw 320 do not have to match theexact thread form and pitch of the housing 330 for operation. The pitchand form of the thread 324 on the bone screw need only be constructedand arranged to threadably pass through the bore 344 without significantinterference between the two components. So long as the screw head 321remains the same size, this feature may also allow theinterchangeability of screws of varying shaft 323 diameter whileutilizing the same housing 330, retainer assembly 313, and fasteners orset screws (not shown). A kit may be provided which includes a housing330, retainer assembly 313, and set screw (not shown), with a pluralityof bone screws 320 having different outer shaft diameters allowing asurgeon to choose a bone screw for the specific patient condition.

The housing 330 may include additional features such as recesses 333 orgrooves 335 for interaction with insertion tools, extension sleeves,reduction tools, etc. The inner surface of the housing 330 at the lowerend thereof may include opposing planar surfaces 334 and opposing curvedsurfaces 336. The planar surfaces 334 may extend further into the bore344 than the remainder of the inner surface of the housing 330. Thecurved surfaces 336 may be configured to mate with the spherical surfaceof the screw head 321, and the planar surfaces 334 may be configured tomate with the planar surfaces 325 of the screw head 321. The screw head321 may be received within the housing 330 in a first orientation or asecond orientation, turned 180 degrees from the first orientation. Themating of the planar surfaces 334 of the housing with the planarsurfaces 325 of the screw head 321 may prevent rotation of the screw 320around the longitudinal axis L-L. See FIG. 28. The mating of the curvedsurfaces 336 of the housing with the spherical surface of the screw head321 may allow movement of the screw head 321 relative to the housing 330with a longitudinal axis of the screw 320 being positionable in any oneof a plurality of angular positions within a single plane relative tothe longitudinal axis of the housing bore 344. The threading 340 on theinner surface of the housing 330 may cross the planar surfaces 334 andthe curved surfaces 336. In some examples, the threading 340 may crossonly the planar surfaces 334.

The bone screw 320 may be inserted through the top of the housing 330with the threaded shank 323 extending out the bottom of the housing 330,as seen in FIGS. 24 and 26. The head 321 of the screw 320 may be held inplace by the retainer assembly 313. As seen in FIG. 26, the retainingring 314 and biasing member 315 are received in an annular space 317defined between an inner wall of the housing 330 and the insert 316,above a lower lip 355 on the insert 316. The structure of the housing330 and retainer assembly 313 in combination with the planar surfaces325 on the screw head 321 may allow pivoting of the screw head 321 in asingle plane with respect to the housing 330.

For simplicity purposes, the following discussion makes reference to thebone anchor 10, however this is not intended to limit the devicesdescribed herein, as the discussion may be applied to the other boneanchors 100, 200, 300.

To lock the elements in place, the practitioner may screw a fastener orset screw not shown into threading 42 at the upper portion of thehousing 30 which may force the rod or elongate member against the uppersurface of insert 16 and in turn may force the insert 16 against thehead 21 of the screw 20. Prior to final tightening of the set screw, thebiasing member 15 may cause the insert 16 to frictionally engage thehead 21 of the screw 20 to resist movement of the housing 30 withrespect to the screw 20. After tightening of the set screw, thefrictional force between the insert 16 of the retainer assembly 13 andthe head 21 of the screw 20 may be sufficient to lock the screw 20 inplace with respect to the housing 30. In some examples, the U-shapedchannel 43 may be deep enough so that the set screw does not force therod against the bottom of the U-shaped channel 43. Alternatively, theretainer assembly 13 may be omitted, and the set screw may force the roddirectly against the head 21 of the screw 20 to secure the screw 20 inplace.

It is to be understood that even though numerous characteristics ofvarious examples have been set forth in the foregoing description,together with details of the structure and function of various examples,this detailed description is illustrative only, and changes may be madein detail, especially in matters of structure and arrangements of partsillustrated by the various examples to the full extent indicated by thebroad general meaning of the terms in which the appended claims areexpressed. This may include, to the extent that it is appropriate, theuse of any of the features of one example being used in other examples.The invention's scope is, of course, defined in the language in whichthe appended claims are expressed.

What is claimed is:
 1. A bone anchor comprising: a housing comprising abore extending therethrough defining an inner surface and a distal endcomprising two opposing arms defining a channel extending transverse tothe bore, the housing further comprising a first set of diametricallyopposed openings disposed therein, each opening extending through thehousing transverse to the bore; a bone screw comprising a head and ashank extending from the head defining a bone screw longitudinal axis,the bone screw positionable within the housing such that the headresides in the housing and the shank extends outside the housing, thehead comprising a spherical surface and a second set of diametricallyopposed openings disposed therein that extend transverse to the bonescrew longitudinal axis and correspond to the first set of diametricallyopposed openings extending through each side of the housing; a pair ofpins, each pin receivable through a respective one of the first set ofdiametrically opposed openings extending through each side of thehousing and a respective one of the second set of diametrically opposedopenings disposed in the head to enable uniplanar movement of thehousing relative to the bone screw; and a multi-part, biasable retainerassembly positionable inside the bore of the housing above the head ofthe bone screw, the retainer assembly comprising a retainer comprisingan inner annular surface for engaging the head of the bone screw and anannular biasing member for biasing the retainer towards the head of thebone screw so that the housing is adjustable to a desired positionrelative to the bone screw prior to receiving a rod in the channel. 2.The bone anchor of claim 1, wherein each of the pair of pins comprisesan outer comprising a first diameter and an inner portion comprising asecond diameter that is less than the diameter of the outer portion. 3.The bone anchor of claim 2, wherein the first set of diametricallyopposed openings disposed in the housing receive the outer portion ofthe pins with a friction fit.
 4. The bone anchor of claim 2, wherein thesecond set of diametrically opposed openings disposed in the headcomprise a diameter that is greater than the diameter of the innerportion of each pin to allow for swinging movement of the head along thebone screw longitudinal axis relative to the pair of pins.
 5. The boneanchor of claim 1, wherein the second set of diametrically opposedopenings disposed in the head are formed from a single throughbore inthe head.
 6. The bone anchor of claim 5, wherein the pair of pinscomprises a single pin extendable through the first set of diametricallyopposed openings disposed in the housing and the single throughbore inthe head.
 7. The bone anchor of claim 1, wherein the bone screw isreceived into the bore from the distal end of the housing.
 8. The boneanchor of claim 1, wherein the inner annular surface further comprises aconcave inner annular surface comprising a radius of curvature matchedto a radius of curvature of the spherical surface of the head.
 9. Thebone anchor of claim 8, wherein the the annular biasing member furthercomprises a wave washer.
 10. The bone anchor of claim 8, wherein theretainer assembly further comprises an annular retaining ring.
 11. Thebone anchor of claim 1, wherein a lower portion of the bore extendingthrough the housing has a thread disposed therein to allow threadsdisposed on the shank to pass therethrough.
 12. A bone anchorcomprising: a housing comprising a bore extending therethrough definingan inner surface and two opposing arms defining a channel extendingtransverse to the bore, the housing further comprising a first pair ofdiametrically opposed openings disposed in a lower portion of thehousing, each opening of the first pair of openings extending throughopposing sides of the housing transverse to the bore; a bone screwcomprising a head and a shank extending from the head defining a bonescrew longitudinal axis, the bone screw positionable within the housingsuch that the head resides in the housing and the shank extends outsidethe housing, the head comprising a spherical surface and a second pairof diametrically opposed openings disposed therein that extendtransverse to the bone screw longitudinal axis and correspond to thefirst pair of diametrically opposed openings extending through the sidesof the housing; a pair of pins, each pin receivable through a respectiveone of the first pair of diametrically opposed openings extendingthrough the sides of the housing and a respective one of the second pairof diametrically opposed openings disposed in the head to enableuniplanar movement of the housing relative to the bone screw; and amulti-part, biasable retainer assembly positionable inside the bore ofthe housing above and in contact with the head of the bone screw, theretainer assembly comprising an annular retainer for engaging the headof the bone screw and an annular biasing member for biasing the retainertowards the head of the bone screw so that the housing is adjustable toa desired position relative to the bone screw; wherein the bone screwand the retainer assembly are configured for top loading into thehousing.
 13. The bone anchor of claim 12, wherein each of the pair ofpins comprises an outer portion comprising a first diameter and an innerportion comprising a second diameter that is less than the diameter ofthe outer portion.
 14. The bone anchor of claim 13, wherein the firstset of diametrically opposed openings disposed in the housing receivethe outer portion of the pins with a friction fit.
 15. The bone anchorof claim 13, wherein the second set of diametrically opposed openingsdisposed in the head comprise a diameter that is greater than thediameter of the inner portion of each pin to allow for longitudinalmovement of the head along the bone screw longitudinal axis relative tothe pair of pins.
 16. The bone anchor of claim 12, wherein the secondset of diametrically opposed openings disposed in the head are formedfrom a single throughbore in the head.
 17. The bone anchor of claim 16,wherein the pair of pins comprises a single pin extendable through thefirst set of diametrically opposed openings disposed in the housing andthe single throughbore in the head.
 18. The bone anchor of claim 12,wherein the annular retainer comprises a concave inner annular surfacecomprising a radius of curvature matched to a radius of curvature of thespherical surface of the head.
 19. The bone anchor of claim 18, whereinthe annular biasing member further comprises a wave washer.
 20. The boneanchor of claim 18, wherein the retainer assembly further comprises anannular retaining ring.
 21. The bone anchor of claim 1, wherein a lowerportion of the bore extending through the housing is constricted inorder to retain the head of the bone screw in the housing.
 22. The boneanchor of claim 1, wherein the retainer assembly comprises a pair ofdiametrically opposed concave part cylindrical surfaces defined on anupper surface thereof for receiving a rod when the surfaces are alignedwith the channel extending transverse to the bore of the housing.